الفهرس 
CHAPTER (2) LITERATURE REVIEWOnly 14 pages are availabe for public view
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Abstract
There is an increasing demand for high-performance heat exchanger devices
used in aerospace vehicles, automobiles, cooling of electronic equipment, power
plants, chemical processes, petroleum industries, etc. This has led to various designs of heat exchangers fitted with internally finned tubes, which have been widely used in many engineering applications to enhance heat transfer coefficient and minimize the required surface area. This study presents an experimental and a 3-D numerical
investigation for internally finned tubes. It involves both continuous and interrupted finned tubes. Water is chosen as the working fluid with the proposed system. Firstly, a test rig was designed and fabricated for examining such finned tubes. The experiments were conducted at Reynolds number varying from 4509 to 11165. Secondly, the numerical investigation was executed by solving the conservation equations of mass, momentum, and energy along with two equation-based realizable K−ε model with enhanced wall treatment for thermal and hydrodynamic. The proposed CFD model was validated with the results available in the present experimental works.
The numerical results showed a good agreement with these experimental ones. Thirdly, the numerical computations were extended to reveal the effect of the different fin dimensions, including fin height, fin-rows number, fin thickness, and interruption length on the performance of internally finned tubes. Finally, a performance evaluation
study was conducted to find out the effectiveness of using these tubes in various engineering applications. The computed parameters involved Nusslet number and friction factor of turbulent fluid flow inside internally finned tubes. In addition, the velocity, temperature, and pressure distribution, streamlines, and thermal enhancement
factor were considered under different operational conditions. from the present study, it has been found that the internally finned tubes have a high thermal performance compared to the finless ones. Hence, for continuous finned tube, it has been found that the average Nusselt number value is enhanced by 40.92 % and the average friction factor rises by 90.05 % when the fin height ratio (H/di) increases from 0.1786 to 0.4018. Also, the average Nusselt number value is nearly
doubled, and the friction factor value is increased about two and half times when the fin row number (N) increases from 2 to 8. On the other hand, for interrupted-finned tube, it has been found that the average Nusselt number value is enhanced by 25.02% and the average friction factor rises by 77.94 % if the fin height ratio (H/di) increases from 0.1786 to 0.4018. Also, the average Nusselt number value is enhanced by 21.49% and the friction factor value is increased by about 60.25% when the fin row number (N) increases from 2 to 6. Furthermore, it has been found that the fin height has the dominant effect on Nusselt number values for the internally-finned tubes compared to
fin-rows number and fin thickness.
As well, it has been found that when the continuous and interrupted-finned
tubes have the same internal surface area, the interrupted-finned tube is preferable compared to the continuous one when the interruption length of the interrupted-finned tube is short. For example, when the number of fins per row (Nfr) is 2, the Nusselt number of the continuous finned tube is higher than that of the interrupted one by 3.1
%. But when it is increased to to 4 fins per row, the Nusselt number of the interrupted finned tube is enhanced by nearly 13.59 % over the continuous finned value. According to the performance evaluation study, it has been found that under the same pressure DROP and internal surface area, both continuous and interrupted finned tubes become thermally useful compared to the finless ones, and the thermal performance factor (TEF) is enhanced with increasing the fin-rows number and fin height, but under same mass flow rate and internal surface area, the opposite is true. Also, the interrupted-finned tube is useful compared to the continuous one when they are operated under the same pressure DROP even if the interruption length is long, and
under the same pumping power but in the case of short interruption length only. On the other hand, if both finned tubes are operated under the same mass flow rate, the interrupted-finned tube becomes the bad choice.